PROJECT SUMMARY Of the retinal degenerative diseases that affect 9 million Americans, cone photoreceptor dystrophies are arguably the most devastating. Gene therapy is a potential means to strengthen photoreceptor viability. However, the first human gene therapy trial for retinal degeneration found improved visual function but did not slow degeneration of photoreceptors. The goal of this gene therapy-oriented proposal is to determine whether therapy is achievable in the context of an already diseased retina and if metabolic reprogramming could be an efficacious treatment option. During the previous funding period, we succeeded in restoring retinal function for more than 11 months in a mouse model of rod degeneration even after the onset of degeneration and at late-stage disease. We now intend to determine whether the same outcomes are achievable in cone-based dystrophies. To do this, we will generate a novel, inducible genetic rescue system in the cone-specific G-protein, guanine nucleotide binding ?- transducin 2 (Gnat2), which will allow us to conditionally reverse GNAT2-deficiency while controlling the temporal and spatial aspects of phenotypic reversal. Using Gnat2floxSTOP/Gnat2CreERT2, we will establish that the model faithfully recapitulates cone-mediated dystrophies (Aim 1). We will restore the model to wild type via tamoxifen injection at early, middle, and late disease stages and assess effects on the rate of degeneration (Aim 2) to determine the temporal limitations of gene therapy. Finally, we will induce metabolic reprogramming and assess its utility as a possible non-gene- specific strategy for treating cone degenerations -based dystrophies (Aim 3). The Gnat2floxSTOP/Gnat2CreERT2 programmable model will provide a platform for contributing to ongoing efforts aimed at increasing restoration of visual function following gene therapy for cone-mediated dystrophies. It will also allow us to address several compelling, clinically relevant questions: Is the brain?s circuitry sufficiently plastic to recover from the pathological changes caused by the Gnat2 mutation? Is there a point of no return after which, despite reversion of the genotype to wild type, cones cannot be salvaged? Can temporal barriers to gene therapy be relieved by metabolic reprogramming? Taken together, this proposal is certain to 1) define the factors limiting interventional therapy; 2) validate a new, inducible model of cone-mediated retinal degeneration; and 3) determine whether metabolic reprogramming can serve as an efficacious, non-gene-specific strategy for treating retinal degeneration.